电子束在α-磁铁模型中传输模拟与优化

在电子直线加速器设计中，α-磁铁通常被用来压缩脉冲长度，采用热阴极微波电子枪和α-磁铁相结合的设计，可以获得皮秒或亚皮秒量级脉冲长度的电子束。电子束在α-磁铁中的传输过程较为复杂，相关文献介绍的研究成果均是基于理想模型，且有镜板开孔的α-磁铁的束流传输研究，对α-磁铁的使用具有重要的指导作用。本文首先简单介绍了用于高能电子成像装置的α-磁铁模型的设计，对电子束在理想模型与α-磁铁模型中传输模拟结果进行对比分析，验证了所构建模型可以有效地实现脉冲纵向压缩的结论。此外，对以优化角度进入α-磁铁和在空间电荷效应影响下的单束团及多束团束流动力学模拟结果进行了讨论，提出通过减小入射角度来补偿α-磁铁镜板上的束流进出孔对束流传输影响的方案。通过在α-磁铁与电子枪之间增加四极磁铁组，优化了束流发射度和束团尺寸。

Simulation and Optimization of Electron Bunches Transport in an Alpha Magnet Model

Thermionic RF gun-based electron accelerators can produce ultrashort electron beams. The alpha magnet is used for bunch compression. The transmission process of electron bunch in the alpha magnet is complicated. The research results described in the related literature were based on the ideal model, and the study of beam transmission in an alpha magnet which have an entrance hole in the mirror plate was important for the use of alpha magnet. The design model of alpha magnet is presented, which is the important part of high energy electron radiography facility. The beam transport properties between the ideal model and the alpha magnet are compared by beam dynamics simulation. It is verified that the designed alpha magnet model can effectively compress the electron bunch length. The beam dynamics under the optimization injection angle and space charge effects was discussed. It was found that the effects of the mirror plate entrance hole can be compensated by reducing the injection angle. The multi-bunch simulation results were also reported. The beam emittances and bunch sizes can be optimized by installing some quadrupole magnets between the thermionic RF gun and the alpha magnet.